Nissan 240SX Repair Question
Reversed the battery cabels
Answer
If you checked all the fuses and they are good, you make have burnt up some fusible links. A fusible link is a wire that acts like a fuse when a short is present. They are connected off of the battery and feed the some of the main circuits. Sometimes it is hard to tell if is blown just by looking at it. When they go, they can be discolored (black or burnt) and soft when you attempt to bend them. However the best way to test them is with a volt meter for a open. I know Nissan used them in their older cars but I don't know if your car has them or if they still use them.
Follow the battery positive cable it will lead you to the power distribution box-open it up you will see the little colored square boxes inspect it you can tell when its blown thru the window.